Mr. Lira and eight others tend an acre plot wedged between the Hilton Hotel and a pair of busy avenues, where lettuce, mint, beets, and other crops thrive. Lira says he has become self-sufficient from his steady share of vegetable sales.

Urban farming's success here is rooted in an unlikely source: visiting agronomists from Cuba. But in a Venezuela extremely polarized over the rule of leftist President Hugo Chávez, these and hundreds of other Cubans working throughout Venezuelan society are sowing the seeds of controversy.

For the government of Mr. Chávez, the Cubans provide invaluable aid in areas where Cuba's socialist revolution has made internationally recognized strides, such as health and education.

But for Chávez's opponents, who have long charged that his goal is to transform Venezuela into a communist dictatorship, the Cuban workers are really preparing the ground for the "Cubanization" of Venezuela. Although the first Cubans came here shortly after Chávez took office in 1999, the controversy has heated up since the launch in recent months of three new programs: urban gardening, literacy training, and medical care for the poor.

Chávez vehemently denies the opposition's charges. But he has praised Cuba, ruled since 1960 by dictator Fidel Castro, where free speech is limited, political opponents are often jailed, and independent media banned. Chávez has met frequently with Mr. Castro, and he once famously called Cuba "a sea of happiness."

The Cuban doctors here as part of the "Inside the Neighborhood" exchange program live and work in many of Caracas's poorest and most crime-ridden neighborhoods, where residents previously had to travel long distances and wait hours for medical care.

In April, Viviana Iglesias left her husband and two children in Matanzas, Cuba, for a one-year stay in a poor community high above downtown Caracas. There, in a small home, she attends patients. A few years back, she did similar work in Haiti.

If the doctors are expelled for political reasons, she says, "it will be a disappointment. We give this aid to many nations and it has always been accepted well."

Neighbors - who praise the work of the several Cuban doctors in the neighborhood - say that they have not received indoctrination. But the Cuban-backed programs have clearly solidified Chávez's support among the poor, who make up some two-thirds of Venezuelans, a key constituency for Chávez should a recall referendum on his presidency take place.

"I never voted for Chávez," says Yajaira Gonzales, whose children Dr. Iglesias treated, "but if there is a vote, I'll back him."

Hector Larreal, president of the National Assembly's health subcommittee and a member of the opposition Democratic Action Party, says the Cuban doctors are not qualified to work in Venezuela, and that they prescribe inappropriate "alternative" medicines and spread communism.

"The worst part about it is that they come with an ideological message to orient the communities toward a failed political system," says Mr. Larreal.

The media, which are overwhelmingly anti-Chávez, have reported on a series of cases of alleged malpractice by Cuban doctors. Critics also say that the urban gardens are contaminated by pollutants, and that the literacy program's goal of teaching 1.5 million people to read is unrealistic. Others even charge that some of the Cubans are spies or paramilitary trainers readying Chávez's most fanatical followers for civil war in case of his downfall. During the 1960s, Venezuela defeated a Cuban-backed guerrilla insurgency. Now some ex-military men fear that the Cubans are back, this time donning hospital whites instead of Army fatigues.

"What they couldn't do [in the '60s], they are doing now ... but this time through politics," charges Vice Admiral Rafael Huizi, founder of an organization of retired military officers.

Back at the urban gardens, Xiomara Hernandez, a business administrator in Caracas, buys freshly harvested lettuce that she says is better and cheaper than that trucked in from the countryside. She sees no menace in the Cuban advisers.

"Professors also come from the United States to teach us things," she says. "Why not accept the good things from a country which has things to teach us?"